1. Field of the Invention
This invention relates generally to implantable medical devices and, more particularly, to methods, apparatus, and systems for a stimulation device with reduced size.
2. Description of the Related Art
There have been many improvements over the last several decades in medical treatments for disorders of the nervous system, such as epilepsy and other motor disorders, and abnormal neural discharge disorders. One of the more recently available treatments involves the application of an electrical signal to reduce various symptoms or effects caused by such neural disorders. For example, electrical signals have been successfully applied at strategic locations in the human body to provide various benefits, including reducing occurrences of seizures and/or improving or ameliorating other conditions. A particular example of such a treatment regimen involves applying an electrical signal to the vagus nerve of the human body to reduce or eliminate epileptic seizures, as described in U.S. Pat. No. 4,702,254 to Dr. Jacob Zabara, which is hereby incorporated in its entirety herein by reference in this specification. Electrical stimulation of the vagus nerve (hereinafter referred to as vagus nerve stimulation therapy or VNS) may be provided by implanting an electrical device underneath the skin of a patient and performing a detection and electrical stimulation process. This type of stimulation is generally referred to as “active,” “feedback,” or “triggered” stimulation. Alternatively, the system may operate without a detection system once the patient has been diagnosed with epilepsy, and may periodically apply a series of electrical pulses to the vagus (or other cranial) nerve intermittently throughout the day, or over another predetermined time interval. This type of stimulation is generally referred to as “passive,” “prophylactic,” or “non-feedback” stimulation.
Among the problems associated with state-of-the-art implantable devices is the fact that the size of the devices may cause discomfort or undesired cosmetic effects in many patients. Thus, there is strong desire in the industry to reduce the size of the implantable devices. However, many attempts to reduce the size of the implantable devices have netted sub-par results. Efforts to produce smaller devices often come with the side effect of reduced ability to perform various stimulation-related functions. This may include various calculation functions, data storage functions, communication functions, the quantity and/or quality of therapy that may be delivered, etc.
One subgroup of implantable devices is neurostimulators, which are used to stimulate nerve tissue. Neurostimulators may be being used to neurological and/or sensory disorders. Typically, neurostimulators require greater energy than cardiac stimulators for effective stimulation of the respective target tissues. This produces a greater challenge to reduce size in neurostimulators since larger devices are needed for stimulators with high energy demands.
Designers have attempted to address the problems associated with large devices by providing devices that are smaller, but containing numerous disadvantages. Often, various functions relating to the operations of an implantable medical device may be sacrificed to achieve a smaller profiled device. Other times, when attempting to reduce the size of the implantable device, the battery life of the device is shortened. This may prompt the need for more frequent surgery.
Another disadvantage of some smaller implantable devices is the fact that it may not contain an integral power source sufficiently robust to perform reliable stimulation delivery for a satisfactory period of time. Other small devices may contain the problem of a rechargeable battery with a minimal charge capacity. This may cause the adverse affect of having to recharge the implantable device too often. Some small devices may require integral non-detachable electrodes which may severely limit the ability to target desirable portions of the patient's body. Generally, the devices that contain larger profiles provide a correspondingly greater amount of milliamp-Hours of charge. On the opposite side of the spectrum, very small implantable devices provide for an extremely small amount of milliamp-Hours of charge. Furthermore, small implantable devices provide for mass versus battery capacity that may result in insufficient Ampere-Hours battery capacity. The devices that provide sufficient Ampere-Hours battery capacity generally require large amount of total mass of the device.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.